A packer is inserted within a casing in a well bore to isolate certain producing zones of a well. The packers normally have an elastomeric seal between the outer circumference of the packer and the inner periphery of the casing for providing a seal between the packer and the casing when the packer is actuated. When a production zone is depleted or it is no longer producing the desired product, it is necessary to remove the packer from the packer and well bore. A packer retrieval tool is normally used to remove the packer as the packer usually can not be easily lifted and removed from the well bore. Slips which bite into the adjacent casing wall are usually employed for anchoring the packer within the casing and it is necessary to disengage the slips from the casing in order to remove the packer. Oftentimes, it is difficult to disengage the slips and a milling tool is required for milling or cutting through the slips. Then, the remainder of the packer can probably be gripped and pulled from the casing. For that purpose, a packer removal tool usually has an upper milling portion for cutting through the slips and a lower removal portion for gripping the remainder of the packer for pulling the packing remains from the bore hole after the slips have been cutaway.
Reference is made to U.S. Pat. No. 4,616,721 dated Oct. 14, 1986 as an example of a packer retrieval tool having an upper bladed portion for positioning above the packer for cutting through the slips, and a lower portion for positioning beneath the packer to grip and pull the packer from the well after removal of the slip and the application of a lifting action against the tool. Gripping fingers on the lower end portion are urged radially outwardly into gripping engagement with the inner periphery of the packer remains for lifting of the packer remains from the well.
As the packer is retrieved from the well, it often sticks in the casing as it is being pulled upwardly from various causes or objects, such as corrosion or dents on the casing walls, formation cuttings not flushed from the bore hole, or junk pieces left in the bore hole. Formation cuttings or junk pieces usually fall into and wedge between the packer and the adjacent casing wall causing intermittent hangups. Such hangups may cause disengagement of the retrieval tool from the packer. In addition, the drill string is raised and lowered during normal operation of the retrieval tool as a result of the removal of drill pipe sections as the drill string and retrieval tool are being lifted from the casing. Such movement likewise may cause the retrieval tool to become disengaged from the packer remains being removed. Further, the retrieval tool may be inadvertently pulled through the packer with the packer left in an intermediate position or falling down the casing to its original position.
U.S. Pat. No. 4,616,721 shows a retrieval tool having a slidable sleeve urged downwardly by a spring and including gripping fingers held in gripping relation against the packer by a releasable ring. Upon a sticking of the packer within the casing, an increased lifting force exerted by a mandrel connected to the tool is transmitted to the release ring through inclined ramps for failure of the ring from hoop tension. Upon a failure of the release ring, upward movement of the tool relative to the sleeve permits inward movement of the fingers into a reduced diameter portion of the tool for release of the tool from the packer. The tool is then withdrawn from the casing without the packer. Thus, the retrieval tool shown in U.S. Pat. No. 4,616,721 cannot be released from the packer unless the release ring fails and the release ring then must be replaced in order for the retrieval tool to be used again.
Other types of packer retrieval tools include a mandrel with lugs that are engaged and disengaged by rotation of the mandrel and this may cause inadvertent disengagement of the packer during the retrieval operation. If desired to disengage the packer, the mandrel is disengaged from the packer and withdrawn through the bore of the packer upon rotation of the mandrel. Thus, manipulation of the drill string is required for disengagement of the retrieval tool from the packer in such tools.